The process of synthesizing nanostructures by chemical vapor deposition (CVD), force instance by the Vapor-Liquid-Solid (VLS) mechanism, involves growth of a rod or tube-like solid nanostructure from a catalyst or seed particle. The particle decomposes gaseous reactive precursors, and under appropriate conditions, the nanostructure grows from the particle. Elongated nanostructures (e.g., rod- or tube-like) can be grown by this method.
While these nanostructures and seed particles are commonly only a few nanometers in diameter, reaction zones in traditional growth systems for nanomaterials, such as tube furnaces, are centimeters to meters in size. In these systems, the growth reactions are often mediated in part by the flow rates, pressure, and temperature established at the macro-scales of the growth chambers, rather than at the micro- and nanoscales of the growth processes. In addition, because the forces experienced by the nanostructures during growth are dominated by phenomena such as thermal vibration, free convection, or surface interactions, growth systems may not be capable of efficiently directing the growth and/or assembly of individual nanostructures, or groups of nanostructures, i.e., into ordered macroscopic configurations (e.g., fibers). Often, localized control of growth conditions is achieved by the location of the catalyst particles, which determine where growth initiates.